1. Field of the Invention
The present invention relates to a process for producing a porous polystyrene gel which is suitable as a chromatography filler by an aqueous suspension polymerization of styrene and divinyl benzene.
2. Description of the Prior Art
In general, porous polystyrene gels obtained by an aqueous suspension polymerization of styrene and divinyl benzene with an organic solvent, have been used in various applications as fillers for a chromatography especially a gel permeation chromatography (GPC).
In the gel permeation chromatography, the porous polystyrene gel is filled in a column and a solution of a sample in a solvent is fed into the column whereby samples having different molecular weights can be separated under the phenomenon that molecules having lower molecular weights are highly diffused into the gel and the discharge of the molecules having lower molecular weights from the column is delayed.
The porous polystyrene gel as the filler for chromatography is obtained by an aqueous suspension polymerization with an organic solvent in a form of beads having a diameter of about 1 to 1000.mu.. The structure of the porous polystyrene gel has three dimentional network structure formed by a crosslinking agent of divinyl benzene and it is the porous material having many pores through the inner parts by the effect of the organic solvent.
Thus, the porous polystyrene gel imparts a function as the filler for a chromatography especially a gel permeation chromatography. The separation factor of the gel is improved depending upon the increase of a volumetric ratio of pores included in the gel. However, the strength of the gel is decreased depending upon the increase of the volumetric ratio of pores. Accordingly, the volumetric ratio of the pores is limited.
On the other hand, the volumetric ratio of the pores in the porous polystyrene gel corresponds to the ratio of the organic solvent included in the preparation of the gel. In accordance with the conventional process for producing the porous polystyrene gel by adding 60 to 67% of an organic solvent, to impart the balanced characteristics of the separation factor and the strength of the gel, it has been difficult to obtain the porous polystyrene gel which can separate standard polystyrenes having a maximum molecular weight of less than 50,000 by the gel permeation chromatography.
Accordingly, it is necessary to decrease the ratio of the organic solvent to the monomers, though the separation factor is decreased. As the result, it has been difficult to obtain a porous polystyrene gel having a satisfactory separation factor and only the gel having inferior separation factor has been obtained.
The inventors have studied to obtain a porous polystyrene gel having an improved separation factor. It has been a common knowledge to minimize an amount of a catalyst in the suspension polymerization. However, the inventors have found that the separation factor of the porous polystyrene gel has been improved depending upon the increase of an amount of the radical polymerization catalyst.
The present invention has been attained by the finding.